Directional backlight
A directional backlight is disclosed. The directional backlight has a plurality of light sources to generate a plurality of input planar lightbeams. The plurality of input planar lightbeams illuminates a directional backplane that has a plurality of directional pixels to scatter the plurality of input planar lightbeams into a plurality of directional lightbeams. Each directional lightbeam has a direction and angular spread controlled by characteristics of a directional pixel in the plurality of directional pixels. The directional backlight can be used to generate a 3D image by specifying the characteristics of the directional pixels in the directional backplane.
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This application is a divisional application of and claims the benefit of priority to parent U.S. patent application Ser. No. 14/309,532, filed Jun. 19, 2014, which is a continuation application of and claims the benefit of priority to prior International Application No. PCT/US2012/040305, filed May 31, 2012, the entire contents of both of which are incorporated herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTN/A
BACKGROUNDThe ability to reproduce a light field in a display screen has been a key quest in imaging and display technology. A light field is the set of all light rays traveling in every direction through every point in space. Any natural, real-world scene can be fully characterized by its light field, providing information on the intensity, color, and direction of all light rays passing through the scene. The goal is to enable viewers of a display screen to experience a scene as one would experience it in person.
Currently available display screens in televisions, personal computers, laptops, and mobile devices remain largely two-dimensional and are thus not capable of accurately reproducing a light field. Three-dimensional (“3D”) displays have recently emerged but suffer from inefficiencies in angular and spatial resolution in addition to providing a limited number of views. Examples include 3D displays based on holograms, parallax barriers, or lenticular lenses.
A common theme among these displays is the difficulty to fabricate displays for light fields that are controlled with precision at the pixel level in order to achieve good image quality for a wide range of viewing angles and spatial resolutions.
The present application may be more fully appreciated in connection with the following detailed description taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:
A directional backlight is disclosed. The directional backlight uses a plurality of light sources to generate a plurality of input planar lightbeams for a directional backplane. The directional backplane is composed of a plurality of directional pixels that guide the input planar lightbeams and scatter a fraction of them into output directional lightbeams. The input planar lightbeams propagate in substantially the same plane as the directional backplane, which is designed to be substantially planar.
In various embodiments, the directional pixels in the directional backplane have patterned gratings of substantially parallel and slanted grooves arranged in or on top of the directional backplane. The directional backplane may be, for example, a slab of transparent material that guides the input planar lightbeams into the directional pixels, such as, for example, Silicon Nitride (“SiN”), glass or quartz, plastic, Indium Tin Oxide (“ITO”), among others. The patterned gratings can consist of grooves etched in the directional backplane or grooves made of material deposited on top of the directional backplane (e.g., any material that can be deposited and etched or lift-off, including any dielectrics or metal).
In various embodiments, the plurality of light sources comprises a plurality of narrow-bandwidth light sources with a spectral bandwidth of approximately 30 nm or less. For example, the narrow-bandwidth light sources may include Light Emitting Diodes (“LEDs”), lasers, and so on. The light sources may include a single-color light source, multiple single-color light sources, three color light sources (e.g., a red LED, green LED, and a blue LED), or three color LED strips, each containing an array of color LEDs (e.g., a strip of red LEDs, a strip of green LEDs, and a strip of blue LEDs).
The plurality of light sources may be arranged in different configurations with respect to the directional backplane to avoid contamination of one light color (e.g., red) into another light color (e.g., blue). In addition, the plurality of light sources may be used with a lens component (e.g., a cylindrical lens, an aspheric condenser lens combined with a cylindrical lens, a microlens, etc.) to collimate and focus the input planar lightbeams into the directional backplane. The plurality of light sources may also be used with a light baffle or absorber to improve efficiency and further focus the input planar lightbeams into the directional backplane.
As described in more detail herein below, each directional pixel in the directional backplane may be specified by a grating length (i.e., dimension along the propagation axis of the input planar lightbeams), a grating width (i.e., dimension across the propagation axis of the input planar lightbeams), a groove orientation, a pitch, and a duty cycle. Each directional pixel may emit a directional lightbeam with a direction that is determined by the groove orientation and the grating pitch and with an angular spread that is determined by the grating length and width. By using a duty cycle of or around 50%, the second Fourier coefficient of the patterned gratings vanishes thereby preventing the scattering of light in additional unwanted directions. This insures that only one directional lightbeam emerges from each directional pixel regardless of the output angle.
As further described in more detail herein below, a directional backplane can be designed with directional pixels that have a certain grating length, a grating width, a groove orientation, a pitch and a duty cycle that are selected to produce a given 3D image. The 3D image can be a red, blue, and green 3D image generated from the directional lightbeams emitted by the directional pixels in the backplane.
It is appreciated that, in the following description, numerous specific details are set forth to provide a thorough understanding of the embodiments. However, it is appreciated that the embodiments may be practiced without limitation to these specific details. In other instances, well known methods and structures may not be described in detail to avoid unnecessarily obscuring the description of the embodiments. Also, the embodiments may be used in combination with each other.
Referring now to
In various embodiments, each directional pixel 125a-d has patterned gratings of substantially parallel and slanted grooves, e.g., grooves 135a for directional pixel 125a. The thickness of the grating grooves can be substantially the same for all grooves resulting in a substantially planar design. The grooves can be etched in the directional backplane or be made of material deposited on top of the directional backplane 120 (e.g., any material that can be deposited and etched or lift-off, including any dielectrics or metal).
Each directional lightbeam 130a-d has a given direction and an angular spread that is determined by the patterned gratings in its corresponding directional pixel 125a-d. In particular, the direction of each directional lightbeam 130a-d is determined by the orientation and the grating pitch of the patterned gratings. The angular spread of each directional lightbeam is in turn determined by the grating length and width of the patterned gratings. For example, the direction of directional lightbeam 130a is determined by the orientation and the grating pitch of patterned gratings 135a.
It is appreciated that this substantially planar design and the formation of directional lightbeams 130a-d upon an input planar lightbeam 115 requires a grating with a substantially smaller pitch than traditional diffraction gratings. For example, traditional diffraction gratings scatter light upon illumination with lightbeams that are propagating substantially across the plane of the grating. Here, the gratings in each directional pixel 125a-d are substantially on the same plane as the input planar lightbeam 115 when generating the directional lightbeams 130a-d. This planar design enables illumination with the light source 105.
The directional lightbeams 130a-d are precisely controlled by characteristics of the gratings in directional pixels 125a-d including a grating length L, a grating width W, a groove orientation angle θ, and a grating pitch L. In particular, the grating length L of grating 135a controls the angular spread ΔΘ of the directional lightbeam 130a along the input light propagation axis and the grating width W controls the angular spread ΔΘ of the directional lightbeam 130a across the input light propagation axis, as follows:
where λ is the wavelength of the directional lightbeam 130a. The groove orientation, specified by the grating orientation angle θ, and the grating pitch or period, specified by Λ, control the direction of the directional lightbeam 130a.
The grating length L and the grating width W can vary in size in the range of 0.1 to 200 μm. The groove orientation angle θ and the grating pitch Λ may be set to satisfy a desired direction of the directional lightbeam 130a, with, for example, the groove orientation angle θ on the order of −40 to +40 degrees and the grating pitch Λ on the order of 200-700 nm.
It is appreciated that directional backplane 120 is shown with four directional pixels 125a-d for illustration purposes only. A directional backplane in accordance with various embodiments can be designed with many directional pixels (e.g., higher than 100), depending on how the directional backplane 120 is used (e.g., in a 3D display screen, in a 3D watch, in a mobile device, etc.). It is also appreciated that the directional pixels may have any shape, including for example, a circle, an ellipse, a polygon, or other geometrical shape. Further, it is appreciated that any narrow-bandwidth light source may be used to generate the input planar lightbeam 115 (e.g., a laser or LED).
Attention is now directed to
Similarly, in
In various embodiments, the input planar lightbeam 225 (265) from the light source 205 (245) can be further collimated into the directional backplane 215 (255) by using a baffle or absorber that regulates the angular divergence of light from the light source 205 (245). This is illustrated in
In additional embodiments, multiple single-color light sources (e.g., lasers or LEDs) may be used to generate multiple input planar lightbeams to illuminate a directional backplane in a directional backlight.
The directional backlights 100-400 illustrated in
The directional backlight may be designed with directional pixels having a set of characteristics such as a specific grating length, grating width, orientation, pitch, and duty cycle. Each directional pixel may be designed to scatter light from a single color into a directional lightbeam. The directional lightbeams generated by all the directional pixels in the directional backplane may be modulated to produce a given red, blue, and green 3D image. In the simplest embodiment, a static 3D image (i.e. a given collection of rays) can be formed simply by suppressing the gratings corresponding to unwanted rays. One can just omit to pattern those gratings during fabrication.
Referring now to
For example,
It is also appreciated that light from LED A may also be scattered by a subset of directional pixels GB 605, however those unwanted rays are outside the intended view zone as long as:
where λA is the wavelength of LED A, neffA is the effective index of horizontal propagation of light A in the directional backplane, λB is the wavelength of LED B (e.g., a green LED, not shown), and neffB is the effective index of horizontal propagation of light B in the directional backplane. In case where the effective indices and wavelengths are substantially the same, Equation 2 reduces to:
For a directional backplane of refractive index n above 2 with LED light propagating near the grazing angle, it is seen that the intended view zone of the display can be extended to the whole space (neff≥2 and sin θmax˜1). For a directional backplane of lower index such as glass (e.g., n=1.46), the intended view zone is limited to about θmax<arcsin(n/2) (±45° for glass).
One skilled in the art would appreciate that the red, blue, and green 3D image may have other colors present if a given color directional lightbeam scatters light into the same direction as a directional lightbeam from another color. Since precise directional and angular control can be achieved with each directional pixel, the directional backlight can be designed to generate many variations of 3D images.
It is further appreciated that the directional backplane 535 shown in
In various embodiments, each color light source may be replaced by an LED strip.
It is appreciated that the directional backlight for use with color LEDs (e.g., directional backlight 500 in
Depending on how each directional pixel in the directional backplane 1020 is configured, i.e., with a given grating length, grating width, orientation, pitch, and duty cycle, the directional lightbeams (e.g., directional lightbeam 1015) form a given 3D image. For example,
A flowchart for generating a 3D image with a directional backlight in accordance with various embodiments is illustrated in
Light from a plurality of light sources (e.g., a single-color light source as in
Advantageously, the precise control that is achieved with the directional pixels in the directional backlight enables a 3D image to be generated with an easy to fabricate substantially planar structure. Different configurations of directional pixels generate different 3D images. In addition, the color light sources can be controlled to produce any desired color effect in the generated images. The directional backlights described herein can be used to provide 3D images in display screens (e.g., in TVs, mobile devices, tablets, video game devices, and so on) as well as in other applications, such as, for example, 3D watches, 3D art devices, 3D medical devices, among others.
It is appreciated that the previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
This application incorporates by reference herein related PCT Patent Application Serial No. PCT/US2012/035573, entitled “Directional Pixel for Use in a Display Screen,” filed on Apr. 27, 2012, which is assigned to the assignee of the present application.
Claims
1. A method of scattering input lightbeams as directional lightbeams with a directional backlight comprising:
- generating a plurality of planar lightbeams from a plurality of light sources;
- inputting the plurality of planar lightbeams into a directional backplane of the directional backlight, the directional backplane having a plurality of directional pixels, each directional pixel having characteristics to control light scattering; and
- scattering the plurality of input planar lightbeams into a plurality of directional lightbeams out of the directional backplane using the plurality of directional pixels, wherein scattering the plurality of input planar lightbeams comprises controlling a direction and an angular spread of each respective directional lightbeam using the characteristics of a respective directional pixel in the plurality of directional pixels,
- wherein an input planar lightbeam from a single one of the light sources is scattered into at least two different directional lightbeams of the directional lightbeam plurality, the at least two different directional lightbeams having different angular directions from one another.
2. The method of scattering input lightbeams as directional lightbeams of claim 1, wherein the light sources of the plurality of light sources are color light sources, and wherein the input planar lightbeam from a single one of the light sources is a planar lightbeam of a single color.
3. The method of scattering input lightbeams as directional lightbeams of claim 1, wherein the at least two different directional lightbeams having different angular directions from one another correspond to different views of a three-dimensional image.
4. The method of scattering input lightbeams as directional lightbeams of claim 1, wherein scattering the plurality of input planar lightbeams further comprises using diffractive scattering, each directional pixel comprising a diffraction grating arranged at a surface of the directional backplane, the light scattering control characteristics of the directional pixel comprising pattern characteristics of the diffraction grating.
5. The method of scattering input lightbeams as directional lightbeams of claim 4, wherein a pattern of the diffraction grating comprises a plurality of substantially parallel and slanted grooves.
6. The method of scattering input lightbeams as directional lightbeams of claim 4, wherein the pattern characteristics of the diffraction grating comprise a grating pitch and a grating orientation configured to control the direction of the directional lightbeam scattered by the directional pixel.
7. The method of scattering input lightbeams as directional lightbeams of claim 4, wherein the pattern characteristics of the diffraction grating comprise a grating length and a grating width configured to control the angular spread of the directional lightbeam scattered by the directional pixel.
8. The method of scattering input lightbeams as directional lightbeams of claim 1, further comprising collimating and focusing the input planar lightbeams into the directional backplane using a lens component disposed between the plurality of light sources and the directional backplane.
9. The method of scattering input lightbeams as directional lightbeams of claim 1, wherein the plurality of directional lightbeams from the directional backplane represent multiple image views that combine to form a three-dimensional image, the different angular directions of the at least two different directional lightbeams corresponding to different ones of the multiple image views.
10. A method of generating a three-dimensional (3D) image with a directional backlight comprising:
- illuminating a directional backplane having a plurality of directional pixels arranged thereon with light from a plurality of color light sources, the light being a plurality of input planar lightbeams, the directional pixels comprising patterned gratings having substantially parallel and slanted grooves;
- scattering the plurality of input planar lightbeams out of the directional backplane as a plurality of directional lightbeams using the plurality of directional pixels, each directional lightbeam having a direction and an angular spread controlled by characteristics of the patterned gratings; and
- generating the 3D image with the plurality of directional lightbeams,
- wherein the directional pixels are configured to scatter light of a single color in an input planar lightbeam from a single one of the color light sources of the plurality of color light sources into at least two different directional lightbeams of the directional lightbeam plurality, the at least two different directional lightbeams having different angular directions from one another corresponding to different views of the 3D image.
11. The method of generating a three-dimensional (3D) image with a directional backlight of claim 10, wherein the characteristics of the patterned gratings comprise a grating pitch and a grating orientation configured to control the directions of the directional lightbeams scattered by the directional pixels.
12. The method of generating a three-dimensional (3D) image with a directional backlight of claim 10, wherein the characteristics of the patterned gratings comprise a grating length and a grating width configured to control the angular spread of the directional lightbeams scattered by the directional pixels.
13. The method of generating a three-dimensional (3D) image with a directional backlight of claim 10, further comprising generating the plurality of planar lightbeams of light from the plurality of color light sources, and
- wherein illuminating a directional backplane comprises collimating and focusing the input planar lightbeams using a lens component disposed between the plurality of color light sources and the directional backplane.
14. The method of generating a three-dimensional (3D) image with a directional backlight of claim 10, wherein the directional backplane comprises a triangular directional backplane.
15. The method of generating a three-dimensional (3D) image with a directional backlight of claim 10, wherein the directional backplane comprises a hexagonal directional backplane and each color light source is disposed on alternating sides of the hexagonal directional backplane.
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Type: Grant
Filed: Aug 31, 2016
Date of Patent: Nov 6, 2018
Patent Publication Number: 20160370594
Assignee: LEIA INC. (Menlo Park, CA)
Inventors: Charles M. Santori (Palo Alto, CA), David A. Fattal (Mountain View, CA), Marco Fiorentino (Mountain View, CA), James A. Brug (Menlo Park, CA), Zhen Peng (Foster City, CA)
Primary Examiner: Jade R Chwasz
Application Number: 15/253,809
International Classification: G02B 27/22 (20180101); G02B 27/14 (20060101); G06T 15/00 (20110101); F21V 8/00 (20060101); G02B 27/42 (20060101);